1. Field of the Invention
The present invention relates to a light source device and a liquid crystal display device employing the same.
2. Related Background Art
Recently, with respect to backlights (light source devices) for use in liquid crystal displays, etc., studies have been directed to backlights in which mercury is not used (a backlight of this type hereinafter sometimes is referred to as mercuryless backlight), in addition to the studies on backlights in which mercury is used. The mercuryless backlight, which does not employ mercury, does not suffer from a decrease in a light emission efficiency caused by a rise of mercury temperature, thereby having an advantage of a quicker start for the emission of luminous fluxes. Further, the mercuryless backlight is environmentally preferable.
As a light source device in which mercury is not used, a discharge lamp device is disclosed that includes a bulb in which a rare gas is sealed, an inner electrode provided inside the bulb, and an outer electrode provided outside the bulb (JP 5(1993)-29085 A). The outer electrode is a linear electrode, and is formed on an outer surface of the bulb so as to be parallel with a central axis of the bulb. By applying a voltage across the inner and outer electrodes, this rare gas discharge lamp device emits light.
Further, a rare gas discharge lamp is disclosed that includes a discharge tube in which a rare gas is sealed, an inner electrode formed inside the discharge tube, and an outer electrode formed spirally on an outer surface of the discharge tube (JP 10(1998)-112290 A).
Furthermore, as a discharge lamp with a rare gas as a principal discharge medium, a discharge lamp is disclosed that includes an air-tight vessel, an inner electrode provided inside the air-tight vessel, and an outer electrode in such a form as a coil form, a mesh form, etc. (JP 2001-325919 A). This publication discloses a method of fixing the outer electrode using a shrinkable tube.
Furthermore, a discharge lamp disclosed in U.S. Pat. No. 5,604,410 includes a discharge tube in which a rare gas is sealed, an inner electrode, and an outer electrode. The inner electrode is formed along a central axis of the discharge tube throughout a substantial entirety of the discharge tube. The outer electrode is a linear electrode, and is formed on an outer surface of the discharge tube so as to be parallel with a central axis of the discharge tube.
However, in the case where a linear outer electrode is formed throughout a substantial entirety of the discharge tube, the discharge is concentrated in the vicinity of the outer electrode, thereby becoming constricted. This sometimes makes it impossible to excite the discharge medium efficiently, sometimes resulting in a decrease in the light emission efficiency. In the case where an outer electrode in a spiral form is provided on an outer surface of a discharge tube, the discharge also tends to be constricted, since the outer electrode is brought into contact linearly with the outer surface of the discharge tube.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a novel light source device, and a liquid crystal display device employing the same.
To achieve the foregoing object, a light source device of the present invention includes: at least one discharge tube; a discharge medium sealed inside the discharge tube; and first and second electrodes for exciting the discharge medium. The first electrode is arranged inside or outside the discharge tube. The second electrode is in contact with an outer surface of the discharge tube at a plurality of contact portions that are located at different distances from the first electrode and are provided discontinuously. A mixture gas containing xenon gas and at least one selected from argon gas and krypton gas is sealed in the discharge tube, the xenon gas accounting for 60 percent by volume (vol %) to 80 vol %. With this light source device, light emission with uniform brightness distribution and high brightness is provided.
In the foregoing light source device, the mixture gas may be a mixture gas of argon gas and xenon gas.
In the foregoing light source device, the discharge medium preferably does not contain mercury.
In the foregoing light source device, the mixture gas may be sealed at a pressure in a range of 13 kPa to 36 kPa.
In the foregoing light source device, the plurality of the contact portions may be arranged in a tube axial direction of the discharge tube.
The foregoing light source device further may include a phosphor layer formed on an inner surface of the discharge tube.
In the foregoing light source device, the discharge tube may include a glass tube, and a dielectric layer formed on an outer surface of the glass tube.
In the foregoing light source device, the second electrode may be in contact with the discharge tube via a dielectric.
The foregoing light source device further may include a supporting plate, wherein the discharge tube is arranged on a side of the supporting plate. In this case, the supporting plate may receive light emitted from the discharge tube, and radiate the same from one principal surface of the supporting plate.
The foregoing light source device further may include a supporting plate, with a plurality of the discharge tubes being held on the supporting plate, the second electrode including a plurality of linear electrodes arranged in parallel on the supporting plate, and the discharge tubes being arranged so as to be perpendicular to the linear electrodes.
Furthermore, a liquid crystal display device of the present invention includes a light source device, and a liquid crystal panel that transmits light emitted from the light source device, wherein the light source device is the above-described light source device of the present invention.